The Ultramafic Flora of the Santa Elena Peninsula, Costa Rica: a Biogeochemical Reconnaissance ⁎ R.D

Journal of Geochemical Exploration 93 (2007) 153–159 www.elsevier.com/locate/jgeoexp

The ultramafic flora of the Santa Elena peninsula, Costa Rica: A biogeochemical reconnaissance ⁎ R.D. Reeves a, , A.J.M. Baker a, R. Romero b

a School of Botany, University of Melbourne, Australia b Department of Chemistry, University of Costa Rica, San Jose, Costa Rica Received 16 October 2006; accepted 9 April 2007 Available online 19 April 2007

Abstract

The Santa Elena peninsula in the northwest of Costa Rica protrudes about 30 km westwards into the Pacific Ocean, and measures about 8–16 km in a north–south direction. Several geological studies have been carried out since 1953, showing that much of the peninsula is made up of peridotite, cut by mafic dykes. Only one previous brief examination appears to have been made of the vegetation in relation to the composition of the soils. We present here the results of a survey of some soils and plants of the eastern part of the peridotite massif, in which 73 plant specimens representing 51 identified species were collected and analyzed. The soils sampled all showed extreme ultramafic characteristics: Fe 10–16%, Mg 4–16%, Ca 0.5–1.4%; Ni 3000– 7500 mg/kg, Cr 1400–3650 mg/kg, Co 150–325 mg/kg. The plants collected include several from genera such as Arrabidaea, Chamaesyce, Helicteres, Hyptis, Lippia, Oxalis, Polygala, Turnera and Waltheria that are also represented on ultramafics elsewhere in the Americas (e.g. Cuba, Puerto Rico, Brazil). Few of the species appear to be endemic to Costa Rica or to the ultramafics of Santa Elena. None of the specimens collected exhibited hyperaccumulation of nickel, the highest Ni concentration being 275 mg/kg in Buchnera pusilla. © 2007 Elsevier B.V. All rights reserved.

Keywords: Costa Rica; Ultramafic flora; Serpentine; Nickel; Biogeochemistry; Santa Elena

1. Introduction silicate mineral serpentine in many ultramafics) have been extensively studied in many parts of the world Soils derived from ultramafic rocks, which are rich in during the last hundred years, leading to a wealth of iron, magnesium and associated trace elements such as knowledge about the limited range of plant species that nickel, cobalt and chromium, have for many years been are able to tolerate the unusual chemical environment of particular interest to scientists working in fields these soils provide. Not only are these soils character- where geochemistry and botany intersect. Ultramafic ized by elevated levels of elements that may be toxic, floras (sometimes referred to as ‘serpentine’ floras, from but the levels of important plant nutrients such as the frequently important presence of the magnesium calcium, potassium and phosphorus are generally unusually low, providing an additional stress factor for plant survival and growth. ⁎ Corresponding author. During the last two decades, several comprehensive E-mail address: [email protected] (R.D. Reeves). publications with worldwide scope (Brooks, 1987;

Roberts and Proctor, 1992; Baker et al., 1992) have dealt peridotites are dominated by diopside-bearing harzbur- with many aspects of serpentine floras: plant inventories gites–lherzolites typically containing 0.5–1.0% Cr2O3 and taxonomy, plant geography, evolution of endemic and 0.2–0.5% NiO, and are richer in Al and Ca than is species, physiology of metal tolerance, and the occa- usual in harzburgites (Desmet, 1985). The geology of sional occurrence of extreme nickel accumulation to this area has been discussed in some detail by Harrison levels exceeding 1000 mg/kg in the plant dry matter (1953), Jager (1977), de Boer (1979), Azéma and (‘hyperaccumulation’). Other publications describe Tournon (1980), Desmet (1985) and Tournon (1994), work carried out on ultramafic floras of a single country amongst others. or region, e.g. New Caledonia (Jaffré, 1980), California Botanical work on the peninsula up to the present (Kruckeberg, 1984), Cuba (Borhidi, 1991). However, time appears to be largely confined to the ongoing there are still large gaps in our knowledge of the species preparation of species inventories for the Parque composition and chemical behavior of serpentine plants Nacional Santa Rosa, and to an unpublished study in many parts of the world, such as in Central America, from the Río Murciélago area (sedimentary–ultramafic Brazil, the Philippines and Indonesia, and there is a need boundary several km north of the area studied here) for more plant collection, taxonomic work and chemical (Balding, 1993). The latter work compared vegetation of analysis of plants and their associated soils from these several 1-m2 quadrats on mudstone with several on areas. serpentine less than 2 km away. Its value is severely One of the two major ultramafic areas of Costa Rica limited by the fact that only 10 of the species found were is on the Santa Elena peninsula on the Pacific coast near identified at the species level. the border with Nicaragua. The peninsula measures Part of the interest in the present study lay in trying to about 30 km E–W and 8–16 km N–S, and falls within determine whether the ultramafics of Santa Elena the Parque Nacional Santa Rosa (approx. 10°40′– supported a significant number of endemic species and 11°00′N; 85°30′–86°00′W; alt. 0–700 m). Although whether any hyperaccumulators of nickel could be sedimentary material covers the northern quarter of the found. In the Caribbean, the rich and largely endemic peninsula, most of the remainder (180 km2) consists of ultramafic flora of Cuba contains the largest number of ultramafic rocks (partially serpentinized peridotites from Ni hyperaccumulators (about 130 species) found any- the Cretaceous) cut by mafic dykes (Fig. 1). The where in the world (Reeves et al., 1996, 1999), mainly

Fig. 1. Geology of the Santa Elena Peninsula, Costa Rica (after Tournon, 1994), showing sampling sites: 1. Potrero Grande; 2.Cerro el Inglès; 3. Playa Naranjo. Geological key: 1. Sedimentary cover; 2. Quaternary ignimbrites; 3. Alluvium (a); 4. Dyke swarm, western coast; 5. Ultramafics (partly serpentinized peridotites); 6. Volcanic and sedimentary series, Potrero Grande and southern coast. R.D. Reeves et al. / Journal of Geochemical Exploration 93 (2007) 153–159 155 on soils that have had a very long continuous period of (Near the top of a ridge above the north- exposure and availability for plant colonization, of the western end of Playa Naranjo.) order of 40 million years. The Santa Elena peninsula is Site 3B: Near 10°48.41′N, 85°41.06′W, altitude described as having the oldest continuously exposed 110 m. (Lower on the hillside, near the ultramafic surface in Central America, estimated at edge of the ultramafic soil area.) 85 million years (Janzen, 1986). This raises the possibility of parallels with the Cuban flora in permit- Soil samples and herbarium and analytical plant ting the evolution of significant numbers of endemics specimens were collected from the serpentine sites and Ni hyperaccumulators. Up to the present time, within the areas noted above. The collection consisted of outside Cuba, only isolated additional cases of Ni 73 plant specimens (56 different species, 51 of which hyperaccumulation have been found in the Caribbean have been identified at species level) and 6 soils. The region: Phyllanthus nummularioides in the Dominican main purpose of the soil collection was to confirm by Republic (Reeves et al., 1996) and Psychotria grandis chemical analysis their ultramafic nature, and the degree in Puerto Rico (Reeves, 2003). to which they correspond in composition to other serpentine soils analyzed from many other parts of the 2. Materials and methods world. Soil samples were in all cases taken from the rooting zone of the herbs and small shrubs, i.e. at 0– 2.1. Sample sites and collection 10 cm depth. Herbarium-quality voucher specimens of all plant In this study, sites chosen for investigation were species in this study were collected in duplicate, with the confined to the eastern part of the peninsula, at altitudes number sequence R.D. Reeves 2547–2618 and 2550A. ranging from 100 to 500 m. The serpentine soils here One set has been deposited at the Herbarium of the are brownish–red soils on hilly relief, mostly moder- Instituto Nacional de Biodiversidad, Santo Domingo de ately deep, much eroded, medium- to heavy-textured, Heredia, Costa Rica, and the other set formed part of the with low fertility. Much of the area supports a savanna Massey University Metallophyte Herbarium, Palmer- or cerrado-type vegetation with grasses dominant; there ston North, New Zealand, which has now been placed in are a few trees, scattered shrubs of 1–3 m and a the care of the Herbarium of the Royal Botanic Garden, moderately rich flora of herbs and low (0.5–1 m) shrubs Edinburgh, Scotland. among the grasses. Rainfall is typically about 1500 mm/yr, and strongly seasonal: there is normally 2.2. Analytical procedures less than 100 mm during the 5- to 6-month dry season between November and May. Sampling was carried out The b2 mm fraction of each soil sample was dried for in January 2003. 2 days at 40 °C, ground and sieved through a 70-mesh Collection sites are summarized by the following sieve to give particles b200 μm in diameter. Accurately data, and are indicated in Fig. 1, which shows the extent weighed subsamples of about 0.15–0.20 g were taken of the ultramafics on the peninsula. for analysis. Total element concentrations were deter- mined by digestion with 12 mL of a 1:1 mixture of Site 1: Potrero Grande. Within 500 m of 10°51.39′N, concentrated nitric and hydrofluoric acids, evaporation 85°40.08′W; altitude 310 m. to dryness, further digestion with 10 mL of concentrated Site 2: Cerro el Inglès: HCl and evaporation to dryness, and final dissolution of 2A: Within 500 m of 10°53.18′N, 85°41.53′ the residue in 10 mL of 2 M HCl. In all cases further W; altitude 506 m. (Both sides of a ridge dilution with 2 M HCl was required for the analysis by overlooking both north and south coasts inductively coupled plasma emission spectroscopy of the peninsula.) (ICP), particularly to ensure that the Fe concentration 2B: Within 500 m of 10°52.52′N, 85°40.47′ in the analyzed solution was kept below 1000 mg/L. The W; altitude 398 m. 20 elements sought were Al, As, B, Ca, Cd, Co, Cr, Cu, 2C: Within 500 m of 10°52.42′N, 85°39.82′ Fe, K, Mg, Mn, Mo, Na, Ni, P, Pb, Sn, Sr, and Zn. W; altitude 361 m. (A shallow basin with The plant material was all washed for several minutes colluvial soils.) in running water within 48 h of collection. After the Site 3: Playa Naranjo: specimens had been dried and identified, they were Site 3A: Within the range 10°48.43′–48.49′N, shipped to Melbourne for removal of material for 85°41.05′–41.07′W; altitude 160–185 m. analysis and for mounting of the remainder as herbarium 156 R.D. Reeves et al. / Journal of Geochemical Exploration 93 (2007) 153–159 specimens. Approximately 0.2 g of leaf/shoot material are: Fabaceae, Poaceae, Asteraceae, Convolvulaceae. was set aside in paper packets for analysis, and 0.05– Only the trees Byrsonima crassifolia (Malpighiaceae) 0.15 g of the air-dried plant tissue was then weighed to and Roupala montana (Proteaceae) and the shrub Rus- ±0.0001 g and digested with 5.0 mL of concentrated selia sarmentosa (Scrophulariaceae) were mentioned in nitric acid in glass tubes in an aluminum heating block the earlier work of Balding (1993). A few local or for 4 h at 110 °C. The digests were allowed to stand regional endemics are included in the collection, e.g. overnight before being diluted with deionized water to a Simsia santarosensis (Asteraceae) and Arrabidaea volume of 7.0, 10.0 or 20.0 mL, depending on the initial costaricensis (Bignoniaceae), but most of the species weight of the sample. The resulting solutions were are of more widespread distribution. The plants analyzed by ICP for 14 elements (Al, B, Ca, Co, Cr, Cu, collected include several from genera such as Arrabi- Fe, K, Mg, Mn, Na, Ni, P and Zn). daea, Chamaesyce, Helicteres, Hyptis, Lippia, Oxalis, Polygala, Turnera and Waltheria that are also repre- 3. Results and discussion sented on ultramafics elsewhere in the Americas (e.g. Cuba and/or Brazil), and some species of even wider 3.1. Soils distribution such as Evolvulus alsinoides and Waltheria indica. All the soil samples showed strongly ultramafic The list of fully identified species is given in Table 2, chemical characteristics (Table 1), with the usual high together with their authorities and the results of the levels of Mg, Fe, Cr, Ni and Co, and low K and P. Ca analyses for a range of elements of most interest. In and Al are quite variable. Many serpentine soils contain addition to the data shown, the following ranges of about 1000–3000 mg/kg total Ni (see, for example, elemental concentrations may be noted (all in mg/kg; Proctor and Woodell, 1971; Vergnano Gambi, 1992). lowest–median–highest): Al 2–70–772; B 19–74–197; The Santa Elena soils are particularly Ni-rich, bearing Mn 8–37–323; Na 59–397–8150; P 51–474–1851; Zn 3000–7500 mg/kg total Ni, comparable with the levels 3–21–95. These are typical ranges found for plants on found in the most strongly ultramafic soils from other ultramafic soils. The median P is lower than that parts of the world (Reeves and Baker, 2000). Cobalt generally found in plants on non-metalliferous soils, levels, as expected, are typically about 20-fold lower reflecting the impoverishment of this element here, as is than those of Ni. The magnesium concentrations are common in serpentines elsewhere. quite variable, but always much higher than those of Ca. In spite of the washing procedures used, there is evidence in the data for a few of the plant samples of 3.2. Plants residual contamination by soil and dust, which can be very difficult to remove from the surfaces of hairy or The natural vegetation was once tropical dry forest, sticky leaves, particularly those of prostrate plants but has been extensively altered by 400 years of human subject to rain-splashed soil. For plants on ultramafic intervention (cutting and burning). Much of the present- soils the presence in any sample of elevated Cr (N20 mg/ day vegetation on the serpentine presents a savanna-like kg), Fe (N1500 mg/kg) and Ni (N150 mg/kg) all appearance, deciduous in the dry season. There are together, provides suspicion of contamination. Such was occasional tracts of taller forest. The 51 species the case with one sample of Oxalis frutescens in which identified in the present work are from 23 different was recorded Cr 52 mg/kg, Fe 6440 mg/kg and Ni families; those most strongly represented (≥4 species) 247 mg/kg; these data were omitted from the averaging

Table 1 Composition of serpentine soils, Santa Elena, Costa Rica Sample a Ni (mg/kg) Co (mg/kg) Cr (mg/kg) Al (%) Ca (%) Mg (%) Fe (%) Mn (mg/kg) Cu (mg/kg) 1 3610 173 2860 2.36 0.90 15.6 10.5 1450 53 2A 5910 325 3640 3.51 1.38 8.3 16.0 2600 72 2B 7220 281 1910 1.81 0.63 12.5 15.2 2260 68 2C1 3240 152 1400 3.61 1.21 3.8 10.2 1520 71 2C2 5290 197 2060 2.86 0.60 11.7 11.5 1810 69 3A 3870 236 1750 2.48 0.47 13.1 11.5 1750 48 Other elements: K: all 0.089–0.313%; P: all 223–416 mg/kg; Pb: all 12–24 mg/kg; Zn: all 101–132 mg/kg. a Key to site locations (see text for details): 1. Potrero Grande; 2. Cerro el Inglès; 3. Ridge above Playa Naranjo. R.D. Reeves et al. / Journal of Geochemical Exploration 93 (2007) 153–159 157

Table 2 Elemental concentrations in plant leaf dry matter (mg/kg) on serpentine soils of Santa Elena (n=number of samples where more than 1) Family Genus and species Ca Co Cr Cu Fe K Mg Ni Ca/Mg n Asclepiadaceae Blepharodon mucronatum Decne. in DC. 11,000 3.7 5.3 6.8 194 5050 7340 48 1.50 Asclepiadaceae Cynanchum schlechtendalii (Decne.) Standley and 9260 0.2 1.7 8.2 175 5670 9350 235 0.99 Steyerm. Asteraceae Ayapana amygdalina (Lam.) R.M. King and H. Robins. 3010 4.4 5.8 10.5 129 9800 13190 94 0.23 Asteraceae Calea prunifolia H.B.K. 9830 2.9 3.5 13.0 71 7010 10300 57 0.95 Asteraceae Melanthera aspera Steud. 6850 0.2 1.7 6.8 224 1400 22510 51 0.30 Asteraceae Simsia santarosensis D.M. Spooner 7810 7.0 8.1 9.9 211 4240 12900 16 0.61 Asteraceae Trixis inula Crantz 12,120 10.0 9.1 25.0 154 4750 16610 24 0.73 Bignoniaceae Arrabidaea costaricensis (Kranzl.) A.H. Gentry 2570 0.1 0.2 6.0 70 5910 5540 13 0.46 Bignoniaceae Arrabidaea mollissima Bureau and K. Schum. in Mart. 938 2.2 3.2 15.1 108 10310 3280 11 0.29 Convolvulaceae Bonamia mexicana J.A. McDonald 8320 0.1 0.5 7.2 71 5120 10170 12 0.82 Convolvulaceae Evolvulus alsinoides L. 8380 0.8 6.1 7.2 279 4340 5180 53 1.62 2 Convolvulaceae Jacquemontia mexicana (Loes.) Standley and Steyerm. 4490 0.4 2.9 7.3 108 4720 8260 23 0.54 2 Convolvulaceae Merremia cissoides Hallier 7300 0.9 3.7 7.6 348 6560 10530 56 0.69 Cyperaceae Bulbostylis paradoxa Nees 746 1.0 2.8 3.5 192 1230 1400 24 0.53 Cyperaceae Eleocharis geniculata Steven 1280 4.3 5.8 7.0 201 6240 9660 15 0.13 Euphorbiaceae Chamaesyce dioica (Hieron) Millsp. 10,070 4.4 18.4 10.3 1610 8560 5700 80 1.77 Euphorbiaceae Mabea montana Muell. Arg. 2940 0.5 2.0 4.7 71 1460 5270 62 0.56 Fab./Caesalpiniac. Chamaecrista hispidula (Vahl) H.S. Irwin and R.C. 4110 4.7 10.7 8.6 646 5670 5420 59 0.76 Barneby Fab./Caesalpiniac. Haematoxylum brasileto Karst. 14,360 0.1 4.8 10.6 100 3200 5430 9 2.65 Fab./Caesalpiniac. Senna pallida (Vahl) H.S. Irwin and R.C. Barneby 28,710 0.7 3.0 4.0 118 4960 4930 13 5.83 Fab./Mimosaceae Calliandra tergemina Benth. 15,160 2.2 3.7 8.4 125 1550 3860 12 3.93 2 Fab./Mimosaceae Mimosa platycarpa Benth. 9660 0.4 2.2 4.0 194 4860 2690 29 3.59 Fab./Mimosaceae Mimosa tricephala Cham. and Schlecht. 7130 0.3 3.0 1.6 287 2300 3150 17 2.27 Fab./Papilionaceae Dalea carthagenensis (Jacq.) Macbride 8150 3.8 7.9 8.4 510 7520 2520 54 3.23 2 Fab./Papilionaceae Diphysa humilis Oerst. ex Benth. and Oerst. 16,360 0.5 0.5 20.2 101 2540 15810 5 1.03 Fab./Papilionaceae Macroptilium gracile (Poepp. ex Benth.) Urb. 22,400 5.6 16.4 9.6 1330 1820 5140 114 4.36 Fab./Papilionaceae Stylosanthes viscosa Sw. 21,360 2.9 8.8 6.7 603 4500 6290 33 3.40 2 Flacourtiaceae Xylosma flexuosa Hemsl. 16,370 1.1 1.3 4.7 32 5650 7490 46 2.19 Krameriaceae Krameria ixine L. 9430 2.6 3.5 7.5 91 12690 6570 42 1.44 2 Krameriaceae Krameria revoluta O. Berg 17,900 4.3 10.6 13.0 709 12320 4530 37 3.95 Lamiaceae Hyptis suaveolens Poit. 5480 3.5 26.6 12.7 3440 5790 8870 175 0.62 Malpighiaceae Byrsonima crassifolia H.B.K. 11,740 6.0 8.1 6.2 98 1720 3640 14 3.12 2 Oxalidaceae Oxalis frutescens Ruiz and Pav. ex G.Don 9580 5.0 15.7 9.8 995 5700 5670 106 1.69 3 Poaceae Aristida ternipes Cav. 1070 2.0 3.9 5.8 190 4150 2370 9 0.45 Poaceae Axonopus aureus Beauv. 1730 0.5 8.9 3.8 486 878 2760 26 0.63 Poaceae Bouteloua repens (Kunth) Scribn. and Merr. 1870 2.3 3.7 5.6 159 6670 1550 11 1.21 Poaceae Paspalum pectinatum Nees 819 4.3 25.0 4.0 3100 4950 1540 170 0.53 Polygalaceae Polygala variabilis H.B.K. 1450 0.1 1.0 5.6 131 2150 3100 42 0.47 Proteaceae Roupala montana Aubl. 1400 0.4 6.4 2.6 122 1760 3400 19 0.41 2 Rubiaceae Diodia teres Walt. 8770 3.4 38.7 3.5 2570 3730 5730 246 1.53 Rubiaceae Randia aculeata L. 3830 0.7 2.9 5.9 61 7100 4290 12 0.89 Sapotaceae Sideroxylon obtusifolium (Roemer and Schultes) T.D. 3520 0.2 1.4 9.8 172 6220 5460 37 0.64 Pennington Scrophulariaceae Buchnera pusilla H.B.K. 3780 2.5 7.5 14.3 607 12130 7500 185 0.50 3 Scrophulariaceae Russelia sarmentosa Jacq. 6280 1.2 6.8 15.3 1360 5340 7140 130 0.88 2 Sterculiaceae Helicteres baruensis Jacq. 6300 0.4 0.6 13.1 143 7190 4820 15 1.31 Sterculiaceae Waltheria indica L. 8610 5.5 6.3 7.6 586 5350 5050 57 1.70 3 Theophrastaceae Jacquinia nervosa C. Presl 4350 0.4 1.7 2.9 96 3690 11410 19 0.38 Trigoniaceae Trigonia rugosa Benth. 3580 0.2 0.4 7.6 46 1430 13410 20 0.27 Turneraceae Turnera diffusa Willd. ex Schult. 5140 4.3 9.5 10.1 517 4090 3260 56 1.58 2 Turneraceae Turnera ulmifolia L. 7620 2.6 21.5 6.2 1920 3890 4930 86 1.55 Verbenaceae Lippia alba N.E. Brown ex Britton and Wilson 11,380 0.1 0.6 3.5 109 5420 5950 33 1.91 158 R.D. Reeves et al. / Journal of Geochemical Exploration 93 (2007) 153–159 shown in Table 2. Using the same criteria, there is some (Jaffré et al., 1979). However, X. flexuosa of Costa Rica doubt about the accuracy of the data shown for a few of does not behave in this way. the other specimens (Hyptis suaveolens, Paspalum Two species found on the Santa Elena serpentines pectinatum, and Diodia teres); if there were any further and which have been reported with high Ni (N1000 mg/ interest in these species, additional analyses with more kg) on serpentine elsewhere are E. alsinoides and W. rigorous washing procedures, including ultrasonic indica. These are species now having pantropical/ vibration, might be needed. subtropical distributions in both hemispheres. E. The low Ca/Mg quotient in serpentine soils has long alsinoides was reported as a hyperaccumulator been considered to be a factor limiting the fertility of (1115 mg/kg) on serpentine soils at Ussangoda, Sri serpentine soils and the ability of some species to Lanka (Rajakaruna and Bohm, 2002). This is quite survive on them (Kruckeberg, 1954; Proctor and surprising in view of the observation that in its Woodell, 1975; Proctor and Nagy, 1992). One conse- occurrences on many ultramafic sites in Queensland, quence of low values of soil Ca relative to Mg, both in Australia (e.g. Glen Geddes, Canoona–Yaamba, Marl- terms of total and extractable concentrations, is a borough Creek) it shows no strong Ni-accumulating generally low value of this quotient in the plant material tendencies, having been found with only 35–75 mg/kg itself, the Ca/Mg quotient on a weight basis in leaf tissue (R.D. Reeves, unpublished data). from serpentine plants frequently falling below 1.0. This W. indica on serpentine in Sri Lanka was surprisingly situation is rarely encountered in plants on other types of found to be a copper hyperaccumulator (Rajakaruna and soils. The Ca/Mg quotient for 51 plant species on Bohm, 2002), while having a normal Ni concentration serpentine here ranged from 0.13 to 5.8 (Table 2)witha of 60 mg/kg. It was, however, reported (as the mean and standard error of 1.46±0.15. This compares synonymous W. americana L.) from serpentine in closely to the value of 1.55±0.28 reported by Balding Venezuela with 1066 mg/kg Ni (Barreto and Casale, (1993) for nine Murciélago serpentine plants, and as 2002). On the other hand, W. indica on serpentine at expected is much lower than her value of 4.72±0.15 for Atkinson Rd., Queensland, contained only 63 mg/kg Ni the (mainly different) set of eight species collected from and 6.3 mg/kg Cu (R.D. Reeves, unpublished data). the nearby mudstone. As in Queensland, these species in Costa Rica, in Ni levels in the Santa Elena serpentine plants ranged spite of the very high total soil Ni concentrations, do not from 5 to 275 mg/kg with a mean and standard error of show abnormal Ni accumulation (70 mg/kg for E. 61.6±8.1 mg/kg (cf. 163±38 mg/kg reported by alsinoides;40–77 mg/kg for three specimens of W. Balding for the collection of nine Murciélago serpentine indica), nor is the Cu concentration of 7.6 mg/kg in W. plants, of which only four were fully identified). indica remarkable. Although Balding reports several Ni levels of 200– 500 mg/kg, these are accompanied by high Fe 4. Conclusions (N1500 mg/kg), providing some suspicion of soil contamination, using the criteria noted above. In the It is clear that the soils of the eastern part of the Santa present work, the maximum Ni concentration of Elena peninsula are strongly ultramafic in their chemical 275 mg/kg was found in a specimen of Buchnera characteristics, with nickel concentrations in particular pusilla, and there is therefore no instance of nickel near the upper part of the range normally found in hyperaccumulation. serpentine soils. It was of special interest to examine the Ni More than 50 fully identified plant species show concentrations in plants of the genera Chamaesyce, chemical compositions that accord with those normally Hyptis, Lippia and Turnera that have furnished found in tropical plants on serpentine. Few local or hyperaccumulators (N1000 mg/kg Ni) on the ultrama- regional endemics have been found: most plants of the fics of Brazil (Brooks et al., 1992). In the Costa Rican eastern areas of the Santa Elena serpentines are species collection, we note the ‘normal’ Ni levels (for tropical of more widespread distribution. No hyperaccumulation serpentine plants) in Chamaesyce dioica (80 mg/kg), H. of Ni was found, even in species or genera that have suaveolens (175 mg/kg), Lippia alba (33 mg/kg) and been reported with high Ni elsewhere (e.g. E. alsinoides two species of Turnera, Turnera diffusa (50, 62 mg/kg) in Sri Lanka, Xylosma species in New Caledonia, Tur- and Turnera ulmifolia (86 mg/kg). The presence of a nera and Lippia species in Brazil), in spite of the very species of Xylosma, Xylosma flexuosa, is interesting long exposure of the Santa Elena ultramafics for floral because of the existence of Ni-hyperaccumulating Xy- evolution. This may be at least partly related to the losma species on the ultramafics of New Caledonia extensive disturbance of the vegetation of the last R.D. Reeves et al. / Journal of Geochemical Exploration 93 (2007) 153–159 159

400 years, causing the present-day vegetation to consist Harrison, J.V., 1953. The geology of the Santa Elena peninsula in of a kind of ‘recovery’ flora. Costa Rica, Central America. Proceedings of the 7th Pacific 2 2 Science Congress, New Zealand, vol. 2, pp. 102–114. This study relates to only a few km of the 180 km Jaffré, T., 1980. Etude écologique du peuplement végétal des sols of ultramafic rocks and soils of Santa Elena. Although dérivés de roches ultrabasiques en Nouvelle Calédonie. Travaux et plant inventory work for the Parque Nacional Santa Documents de l'ORSTOM 124, Paris. Rosa is proceeding, large areas of the peninsula remain Jaffré, T., Kersten, W., Brooks, R.R., Reeves, R.D., 1979. Nickel biogeochemically uninvestigated, and the possibility of uptake by Flacourtiaceae of New Caledonia. Proceedings of the Royal Society of London. B, Biological Sciences 205, 385–394. finding new endemic species and/or nickel hyperaccu- Jager, G., 1977. Geologia de la mineralizaciones de cromita al este de mulator species remains. la peninsula de Santa Elena, Prov. de Guanacaste, Costa Rica Thesis, Escuela Centroamericana de Geologia, San José. Acknowledgements Janzen, D.H., 1986. Guanacaste National Park: tropical ecological and cultural restoration. EUNED FPN-PEA. San Jose, Costa Rica. Kruckeberg, A.R., 1954. The ecology of serpentine soils. Plant species The authors are grateful for the co-operation of Roger in relation to serpentine soils. Ecology 35, 267–274. Blanco Segura and other staff of the Area de Conserva- Kruckeberg, A.R., 1984. California Serpentines: Flora, Vegetation, ción Guanacaste in the Parque Nacional Santa Rosa, to Geology, Soils, and Management Problems. University of Diego Vargas, A. Rodriguez, Giselle Tamayo, and California Press, Berkeley, CA, USA. several other staff of the National Institute for Proctor, J., Nagy, L., 1992. Ultramafic rocks and their vegetation: an overview. In: Baker, A.J.M., Proctor, J., Reeves, R.D. (Eds.), The Biodiversity (INBio), Santo Domingo de Heredia, Vegetation of Ultramafic (Serpentine) Soils. Intercept Ltd., And- Costa Rica, for assistance with plant identification, over, UK, pp. 469–494. and to Augustine Doronila, University of Melbourne, Proctor, J., Woodell, S.R.J., 1971. The plant ecology of serpentine: I. for assistance with the ICP analysis of the plants. Serpentine vegetation of England and Scotland. Journal of Ecology 59, 375–395. Proctor, J., Woodell, S.R.J., 1975. The ecology of serpentine soils. References Advances in Ecological Research 9, 255–366. Rajakaruna, N., Bohm, B.A., 2002. Serpentine and its vegetation: a Azéma, J., Tournon, J., 1980. La péninsule de Santa Elena, Costa Rica: preliminary study from Sri Lanka. Journal of Applied Botany 76, un massif ultrabasique charrié en marge pacifique de l'Amérique 20–28. Centrale. Comptes rendus de l'Académie des Sciences, Paris 290, Reeves, R.D., 2003. 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